Semiconductor manufacturers typically test their semiconductor devices prior to shipping. Such tests may involve electrically probing and exercising the semiconductor devices under a variety of thermal conditions (e.g., over a wide temperature range) to identify faulty devices, to find out-of-tolerance devices and to categorize the devices into various grades (e.g., according to maximum operating speed, according to the amount of usable memory, etc.).
Such testing is useful for a variety of reasons. For example, in some situations, a manufacturer may be able to detect and repair faulty or out-of-tolerance devices (e.g., cure minor defects using a laser at a repair station) thus improving manufacturing yields. Additionally, the manufacturer may be able to charge a premium for devices having exceptionally high maximum operating speeds and/or exceptional amounts of usable memory.
Some manufacturers employ an automated test equipment (ATE) handling system (or simply xe2x80x9chandlerxe2x80x9d) to test semiconductor devices. Some handlers are capable of testing an assemblage having multiple semiconductor devices attached thereto, e.g., lead frames that support multiple electrically-isolated and packaged integrated circuit (IC) devices, strips of devices having Ball Grid Array (BGA) packages, configurations of other chip scale packaging (CSP) devices, and the like. A well-known general term for such an assemblage is xe2x80x9ca panelxe2x80x9d.
A typical handler includes a temperature soak assembly, a test assembly, a temperature desoak assembly, and robotic equipment which moves panels from one assembly to another in a pipelined manner. In general, the temperature soak assembly is configurable to raise or lower the temperature of the panels to a predetermined temperature (a process commonly known as xe2x80x9ctemperature soakingxe2x80x9d) prior to testing. The test assembly is typically capable of testing the semiconductor devices of the panels while maintaining the panels at the predetermined temperature (e.g., by lowering a bed of nails onto particular locations of the panels to test the devices individually). The temperature desoak assembly is typically an area of the handler where the temperature soaked and tested panels reside while returning back to a temperature which is suitable for further processing and handling (a process commonly known as xe2x80x9ctemperature desoakingxe2x80x9d). For example, the temperature soaked and tested panels can be moved to a location where they are simply allowed to idly sit and move to a near-ambient temperature (e.g., near room temperature) in an inactive manner.
Typically, at any one particular time, a manufacturer configures a handler to exclusively perform either a low temperature test or a high (or elevated) temperature test. In the low temperature test, the manufacturer configures the temperature soak assembly of a handler to lower the temperature of the panels to a predetermined low temperature (e.g., xe2x88x9255 degrees Celsius). For example, the manufacturer can connect cooling members of the temperature soak assembly to a cooling source (e.g., to a cryogenic source such as liquid nitrogen, to a refrigerant or cold oil circulator, etc.). Accordingly, panels sitting on the cooling members of the temperature soak assembly move to the predetermined low temperature from their initial temperature (e.g., room temperature, ambient factory temperature, etc.). During low temperature testing, the robotic equipment moves a temperature soaked panel (i.e., cooled panels) from the temperature soak assembly to the test assembly, and lowers a bed of nails onto the panel to individually test the devices of the panel. The robotic equipment then moves the cooled and tested panel from the test assembly to the temperature desoak assembly. A typical approach to heating up the cooled and tested panel in the temperature desoak assembly is to let the panel simply absorb heat from the surroundings (i.e., to idly sit at room temperature in an inactive manner). After the panel moves to a safe handling temperature, the panel is ready for further processing, e.g., the manufacturer can then reconfigure the handler to perform high temperature testing, or move the panels to a similar handler that is already configured for high temperature testing.
In the high temperature test, the manufacturer configures a temperature soak assembly of a handler to raise the temperature of the panels to a predetermined high temperature (e.g., 155 degrees Celsius). For example, the manufacturer can power heating elements within the temperature soak assembly to raise the temperature of the panels to the predetermined high temperature. During high temperature testing, the robotic equipment moves a heated panel from the temperature soak assembly to the test assembly, and lowers a bed of nails onto the panel for electrical testing. The robotic equipment then moves the heated and tested panel from the test assembly to the temperature desoak assembly so that the panel can cool down for further processing (e.g., labeling and storage in gravity feed handlers or other device-carriers, etc.). A typical approach to cooling down the heated and tested panel is to let them simply dissipate heat into the surroundings (i.e., placing the panel in a room temperature environment to idly cool down close to room temperature in an inactive manner).
If the manufacturer attempts to handle the heated and tested panels before the panels have significantly cooled, the manufacturer runs the risk of damaging the panels and/or the handling and processing equipment.
One conventional handler does not wait for panels to move back to a suitable handling temperature by simply exposing the panels back to a room temperature environment in an idle manner. Rather, the temperature desoak assembly of that handler includes a set of thermo-electric elements (i.e., ceramic or plastic electronic components) that actively heat or cool the panels. Each thermo-electric element has a first side and a second side, and receives direct current. When the direct current flows in a first direction through the thermo-electric elements, the first sides of the elements become hot and the second sides become cold. However, when the direct current flows in a second direction through the thermo-electric elements (i.e., the direction opposite the first direction), the first sides of the elements become cold and the second sides become hot.
The operation of the above-described conventional handler with thermo-electric elements will now be described. During a low temperature test, the thermo-electric elements of the temperature desoak assembly receive current in the first direction so that the first sides of the elements become hot. The robotic equipment of the handler moves cooled and tested panels from the test assembly of the handler onto the first sides of the thermo-electric elements to heat them up to a suitable handling temperature. Since the first sides of the thermo-electric elements are hot, the panels reach a suitable handling temperature more quickly than they would if simply exposed to a room temperature environment to idly warm up in an inactive manner, i.e., to simply absorb heat from the surrounding room temperature environment.
Similarly, during a high temperature test, the thermo-electric elements receive current in the second direction so that the first sides of the elements become cold. Accordingly, the robotic equipment of the handler moves heated and tested panels from the test assembly onto the first sides of the thermo-electric elements to cool them down to a suitable handling temperature. Since the first sides of the thermo-electric elements are cold, the panels reach a suitable handling temperature more quickly than they would if simply exposed to a room temperature environment to idly cool off in an inactive manner, i.e., to simply dissipate heat to the surrounding room temperature environment.
Recall that the second sides of the thermo-electric elements become hot in order for the first sides to become cold. To facilitate heat dissipation from the second sides of the thermo-electric elements, the manufacturer can mount heat sinks to the second sides of the thermo-electric elements. In such a situation, the thermo-electric elements reside between the heated and tested panels and the heat sinks. That is, the thermo-electric elements physically separate the heated and tested panels from the heat sinks with the cold first sides of the thermo-electric elements facing the heated and tested panels, and the hot second sides facing the heat sinks. An automated test equipment handling system, which is similar to the above-described handler having thermo-electric elements, is provided by Micro Component Technology, Inc. of St. Paul, Minn.
Unfortunately, there are deficiencies to the above-described approaches to thermally conditioning and testing panels within a handling system. For example, the approach of allowing panels to idly temperature desoak in an inactive manner (e.g., allowing the panels to simply dissipate or absorb heat by placing them in a room temperature environment for a period of time) requires an excessive amount of time and can thus become a bottleneck to throughput of the handler. That is, panels that are temperature desoaking (i.e., cooling off or heating up) in the temperature desoak assembly prevent other panels which have been temperature soaked and tested from exiting the testing assembly thus limiting the overall number of panels that can be tested by the handler in a particular amount of time.
To avoid such a bottleneck, a manufacturer may consider handling the panels without temperature desoaking them (i.e., before the panels have reached a safe and acceptable handling temperature). Unfortunately, handling the panels before they reach an acceptable handling temperature can result in damage to handling equipment and/or the panels themselves. For example, after a high temperature test, if panels are removed from the temperature desoak assembly prematurely and placed on a rubber conveyor assembly (e.g., for further processing at another station), the panels may still be hot enough to melt portions of the conveyor (e.g., rubber belts) thus destroying the conveyor and possibly damaging the panels (e.g., contaminating the panels with melted rubber). Also, the panels may still be too hot for further processing such as for marking (e.g., using a laser) or inspection (e.g., lead/ball inspection). Alternatively, after a low temperature test, the panels may be too cold causing excessive condensation (moisture) to accumulate over packaging of individual devices within the panels making the devices unsuitable for immediate subsequent processing.
Additionally, in the above-described conventional handler having a set of thermo-electric elements, running the thermo-electric elements (as well as cooling the thermo-electric elements when the thermo-electric elements temperature desoak panels after an elevated temperature test) increases the power consumed by the handler. Furthermore, cooling the thermo-elements after an elevated temperature test has an undesirable result of dissipating more heat into the factory. In some situations (e.g., when the handler powers heating elements in the temperature soak assembly to heat panels prior to testing) the additional power requirements of the thermo-electric elements makes the power requirements of the handler, as a whole, excessive and perhaps even impractical. Moreover, thermo-electric systems (i.e., the thermo-electric elements and related control and power circuitry) typically are complex and expensive devices which increase the overall cost and complexity of the handler, and such elements often require periodic maintenance or replacement.
Furthermore, some manufacturers may consider simply blowing air from the external surroundings of the handler over the panels to temperature desoak the panels more quickly than simply allowing the panels to idly sit in still air and temperature desoak (i.e., absorb or dissipate heat). Unfortunately, the air from the external surroundings of the handler can be significantly higher in moisture and dust content than the air within the temperature soak and test assemblies, and blowing such air risks generating condensation on the panels and/or contaminating the panels with dirt. Accordingly, simply blowing air from the surroundings over the panels is typically avoided.
Additionally, some manufacturers may be tempted to rest heat soaked and tested panels on a base, and apply a coolant (e.g., a cryogen, a refrigerant, a cold oil, etc.) through the base to cool the panels. Although such a coolant is often used in temperature soak assemblies for low temperature testing, using such a coolant in a temperature desoak assembly for temperature desoaking in a high temperature test can be somewhat excessive for a temperature desoaking task. For example, it can be extremely cumbersome to haul out and hookup a tank containing a cryogen such as liquid nitrogen. Additionally, using such a cryogen can be extremely messy (e.g., due to frost build up at the hookup point). Also, the use of a cryogen raises the possibility of causing serious human injury (e.g., cold burns) if handled improperly. Furthermore, since liquid nitrogen at room temperature becomes nitrogen gas which can displace breathable oxygen, the use of liquid nitrogen requires additional expensive precautions (e.g., gas sensors, alarms, special employee training, etc.). Additionally, refrigerant systems are complex and expensive to use and maintain. Accordingly, manufacturers can be reluctant to cool down heated and tested panels using a base through which coolant circulates.
In contrast to the above-described approaches to handling panels within a handling system, the present invention is directed to techniques for processing a semiconductor structure using a heat sink which defines a surface which is configured to thermally couple with the semiconductor structure. As such, temperature desoaking of the semiconductor structure can simply involve directing a fluid (e.g., factory air) over the heat sink to bring the temperature of the heat sink (and thus the semiconductor structure) toward the temperature of the fluid (e.g., toward room temperature) making the semiconductor structure safe for further handling and processing. Such techniques can desoak the semiconductor structure more quickly (i.e., at a faster rate) than simply waiting for the semiconductor structure to idly desoak in an inactive manner (i.e., dissipate or absorb heat while simply sitting in a room temperature environment). Additionally, such techniques require less power than the earlier-described conventional handler that requires powering a set of thermo-electric elements.
One arrangement of the invention is directed to a semiconductor handling system having: (a) a temperature soak assembly to temperature soak a semiconductor structure (e.g., a panel); (b) a test assembly to test the semiconductor structure; and (c) a temperature desoak assembly to temperature desoak the semiconductor structure. The temperature desoak assembly includes (i) a heat sink that defines a surface which is configured to thermally couple with the semiconductor structure, (ii) a fluid guide coupled to the heat sink, and (iii) a fluid controller coupled to the fluid guide. The fluid controller provides a fluid (e.g., room temperature air) which the fluid guide directs over the heat sink to bring a temperature of the heat sink to a temperature of the fluid. This arrangement provides an effective low cost and low power means for temperature desoaking a semiconductor structure. Use of the heat sink facilitates temperature change of the semiconductor structure (heat absorption or heat dissipation) more quickly than desoaking the semiconductor structure by simply exposing the semiconductor structure to a room temperature environment and allowing them to idly sit for a period of time.
It should be understood that the thermal heat-transfer resistance between the semiconductor structure and the heat sink (e.g., a flat metal surface) is much lower than that between the semiconductor structure and air. In particular, for a solid-to-solid surface contact, the thermal resistance can be approximately of the order 0.00033 m{circumflex over ( )}2degC/W. In comparison, for a solid-to-air contact, the thermal resistance can be closer to 0.02 m{circumflex over ( )}2 degC/W. Accordingly, temperature desoaking the semiconductor structure through the heat sink is superior to simply waiting for the semiconductor structure to idly exchange heat with the surrounding air.
In one arrangement, the fluid controller of the temperature desoak assembly includes a fan assembly that generates an air stream which the fluid guide directs over the heat sink. The use of air as the fluid alleviates the need for using potentially hazardous and expensive materials such as a cryogen (e.g., liquid nitrogen which can cause human injury if handled improperly and which can become nitrogen gas that displaces oxygen) or a refrigerant, which some manufacturers may be tempted to use to desoak heated and tested panels.
In one arrangement, the surface defined by the heat sink is substantially planar, and the fluid guide is configured to guide the air stream (e.g., room temperature air) over the heat sink in a direction that is substantially perpendicular to the surface defined by the heat sink. This arrangement enables heat-transfer enhancement since the substantially perpendicular angle of incidence results in (i) a high level of mixing and turbulence and (ii) a thorough application of the air stream to the heat sink. In other arrangements, the air stream flows down the length of the heat sink, and/or the air stream through the heat sink substantially results in a laminar flow.
In one arrangement, the fluid guide includes a shroud coupled to the heat sink. The shroud of the fluid guide and the heat sink define a chamber to substantially prevent air of the air stream from directly reaching the semiconductor structure. Accordingly, any moisture or debris (dust, dirt, etc.) in the air of the air stream can be prevented from escaping the chamber and contaminating the semiconductor structure. Preferably, the air of the air stream does not directly mix with controlled test air directly surrounding the semiconductor structure when the semiconductor structure is within the temperature soak assembly, the test assembly and the temperature desoak assembly.
In one arrangement, the fluid guide defines an air stream input port at a first location, and an air stream output port at a second location. Although the first and second locations can be near each other, the first and second locations are preferably separated from each other and/or the output port directs the air stream away from the input port so that there is little or no direct recycling of the exhaust air back into the temperature desoak assembly. For example, in one arrangement, the first location has a height that is lower than that of the second location. Since hot air tends to rise, the air entering the fluid guide at the first location (i.e., the lower location) tends to be lower in temperature thus improving the temperature lowering capabilities of the temperature desoak assembly when desoaking heated and tested semiconductor structures.
In one arrangement, the fan assembly of the fluid controller includes a first fan, coupled to the input port defined by the fluid guide, that blows air of the air stream toward the heat sink; and a second fan, coupled to the output port defined by the fluid guide, that draws air of the air stream away from the heat sink. This arrangement provides a consistent air stream with adequate air pressure throughout (e.g., with minimal air pressure losses). In other arrangements, the fan assembly includes other fan configurations (e.g., multiple fans at the input port, multiple fans at the output port, one or more fans in intermediate portions of the fluid guide, combinations thereof, etc.).
In one arrangement, the semiconductor handling system further includes a set of heating elements, embedded within the heat sink, to raise the temperature of the heat sink. The heating elements enable the system to temperature desoak the semiconductor structure more quickly after a low temperature test.
In one arrangement, the first and second fans of the fan assembly run only during an elevated temperature test in order to cool the semiconductor structure. In another arrangement, the first and second fans of the fan assembly are configured to provide the air stream regardless of whether the temperature of the heat sink is higher or lower than a temperature of the air stream. In this other arrangement, when the temperature of the heat sink is higher than the temperature of the air stream (e.g., due to a heated and tested semiconductor structure thermally coupled thereto), the fan assembly removes heat from the semiconductor structure to temperature desoak the semiconductor structure. When the temperature of the heat sink is lower than the temperature of the air stream (e.g., due to a cooled and tested semiconductor structure thermally coupled thereto), the fan assembly can provide heat to the semiconductor structure to temperature desoak the semiconductor structure. If the handling system employs heating elements to temperature desoak the semiconductor structure after a sub-ambient temperature test, the fans can still be operated in order to prevent the exhaust air from the temperature desoak assembly from getting too cold (a potential annoyance to users of the semiconductor handling system, bystanders, etc.).
In one arrangement, the fluid controller further includes an air filter, proximate to the input port defined by the fluid guide, to filter air of the air stream. Accordingly, debris such as dirt and dust can be removed from the air of the air stream thus preventing such debris from clogging the heat sink and interfering with air flow.
The features of the invention, as described above, may be employed in handling systems, devices and methods, as well as other ATE apparatus, such as those of Teradyne, Inc. of Boston, Mass.